1. Field of the Invention
The present invention relates to a photomask.
2. Related Art
In a process for producing a semiconductor device a display and others, patterns written on a photomask are transferred to a wafer, a substrate of display panel, and others. Namely, the steps for transferring patterns of a photomask to a wafer, a substrate of display panel, and others, are carried out beginning from an application of a photo resist onto a wafer, a base of display panel, and others; carrying out a demagnification projection by means of a stepper; developing the photo resist to form a mask; and etching a liner or under a film through a photo resist as a mask and thereafter removing unnecessary areas of the photo resist.
It is said that large-scaled amorphous silicon TFT and LCD devices used as the display of a notebook personal computer and a desktop personal computer, are produced through five to six of steps of patterning made by photo etching a substrate of the TFT. Therefore, it is required that these steps of photolithography are simplified to reduce the cost of production.
However, there is a limit in the simplification of steps of photolithography in a conventional system for transferring patterns to a wafer and others, by transmitting or shielding projected light through shielding patterns on a photomask, when the shielding patterns are present or not.
It is an object of the present invention to provide a photomask that enables the simplification of steps of photolithography.
Inventors made a study in order to attain the above-mentioned object. As a result, inventors found that projecting a number of rays to a wafer based on the area becomes possible through a conventional photomask having shielding pattern films made of shielding metallic thin film formed on a transparent substrate. The photomask is further provided with translucent patterns made of translucent metallic thin film including mainly tantalum. The tantalum is made from materials selected from tantalum silicide, tantalum oxide, tantalum nitride or a mixture thereof. The steps of projection and development made using the photomask bring about a difference in solubility between a part of resist corresponding to shielding patterns and a part of a resist corresponding to translucent patterns by which a resist pattern comprised of a portion of patterns having the thickness of resist patterns formed ordinarily and a portion of thinner patterns can be formed. It is then possible to make two species of patterning in one photomask so that the reduction of the number of masks is realized. The inventors made the present invention based on the basis of the above-mentioned knowledge.
Namely, the present invention, as mentioned in claim 1, is a photomask provided with shielding patterns made of shielding metallic thin film on a transparent substrate, wherein the photomask further comprises translucent patterns mainly including tantalum of materials selected from tantalum silicide, tantalum oxide, tantalum nitride or mixture thereof.
Layers formed on an insulating substrate, according to the present invention, can be formed into patterns through the steps of overlaying the layers with a resist pattern comprised of a part of patterns having the thickness of resist pattern formed ordinarily and a part of patterns made of thin film, etching the layers through the resist pattern so that the layers are formed into patterns, thereafter removing the part of patterns made of thin film by O2 ashing and the like so that a part of the layer covered with the part of patterns made of thin film is exposed, and further etching a part of the exposed layer by which the number of steps of photolithography can be reduced.